Specifying "good" nutrition or the appropriate level of nutrients is dependent upon our knowledge of how the body regulates flows and stores of the critical elements of energy and protein metabolism in health and disease. The longterm goals of this protocol are to elucidate how the body regulates amino acids and protein, how it handles dietary intake, and how other nutrients (e.g. carbohydrate and fat) interact with them. Our approach has been to administer stable isotopically labeled amino acid tracers to determine amino acid and protein kinetics in healthy individuals. The primary arm is the determination of amino acid metabolism in normal individuals to define normal physiology which can be applied to the understanding of amino acid metabolism in states of pathophysiology (e.g. injury or metabolic disease). This protocol has 2 aims: (1) To define how individual amino acids in the diet are utilized by the splanchnic bed. (2) To define the role of hormones in regulating the uptake and utilization of amino acids.Epinephrine acutely lowers amino acid levels not by decreasing proteolysis and amino acid appearance but by increasing disappearance of amino acids by oxidative disposal. Epinephrine causes a sustained increase in energy expenditure with continued exposure to elevated epinephrine levels, and this increase in energy expenditure is largely fueled by fat oxidation.